This invention relates to solvent extraction processes in general and more specifically to a process for separating the organic phase from the aqueous phase in a solvent extraction process for removing copper from raw ore.
The overall efficiency of a copper mining operation depends in part on the techniques which are used to separate the copper from the raw ore. Many different methods have been developed over time to accomplish copper removal with a maximum degree of effectiveness. Of primary interest are various techniques which are collectively known as xe2x80x9csolvent extraction,xe2x80x9d or xe2x80x9cSXxe2x80x9d for short, in which copper ions are leached or otherwise extracted from raw ore using chemical agents. Solvent extraction processes for removing copper ions are described in detail in U.S. Pat. No. 5,733,431, entitled xe2x80x9cMethod for Removing Copper Ions from Copper Ore Using Organic Extractionsxe2x80x9d which is incorporated herein by reference for all that it discloses.
Most solvent extraction or SX processes currently being used in the copper industry utilize a multi-stage process in which the raw ore is first contacted with an initial leaching solution or lixiviant. Representative lixiviants include, but are not limited to, sulfuric acid, acidic chloride solutions, nitrate solutions, ammonia, and ammonium salt compositions. The lixiviant leaches copper ions from the ore to generate a lixiviant product which consists of a copper ion concentrate (also known as a xe2x80x9cpregnant leach solutionxe2x80x9d). The lixiviant product/copper ion concentrate is thereafter combined (e.g., mixed) with an organic extractant. The organic extractant removes the copper ions from the lixiviant product to generate a copper ion-rich organic solution. Many different organic extractants exist and may be obtained from any of a wide variety of commercial sources. By way of example, most commercially available organic extractant compositions typically consist of a mixture containing about 90-95% of a petroleum dilutant (e.g., kerosene or tridecanol) and about 5-10% hydroxyphenyl oxime. Prior to the combination of the organic extractant and the lixiviant product, the organic extractant will contain little or no copper ions therein (depending on whether a fresh or recycled extractant supply is involved) and is also known as a xe2x80x9cbarren organic extractantxe2x80x9d. During the mixture of these components, copper ions within the lixiviant product are transferred directly into the barren organic extractant. As a result, an organic phase and an aqueous phase are produced. The organic phase (also known as a xe2x80x9cloaded organic extractantxe2x80x9d) consists of the organic extractant which contains copper ions extracted from the lixiviant product. The aqueous phase (also known as a xe2x80x9craffinatexe2x80x9d) consists of the lixiviant solution which lacks any substantial or appreciable amounts of dissolved copper therein. The organic phase is thereafter separated from the aqueous phase and is retained for further processing to extract the copper. The aqueous phase (i.e., raffinate) may be discarded, stored for future use, or immediately reused on additional amounts of ore.
A significant problem associated with the foregoing process relates to the separation of the organic phase (i.e., the loaded organic extractant) from the aqueous phase (i.e., the raffinate). While the two phases tend to separate into discrete layers based on substantial differences in polarity and other physical factors (e.g., specific gravity), as a matter of practice, some aqueous tends to remain with the loaded organic extractant and vice-versa. The presence of the aqueous phase in the organic phase can cause problems later on during the electrowinning process in which the copper is plated onto a cathode. For example, in some SX processes, the presence of the aqueous phase in the organic phase has the effect of transferring chloride into the pregnant electrolyte. In other processes, aqueous entrainment in the loaded organic has the effect of transferring iron to the pregnant electrolyte. Each contaminate has a negative effect on cathode quality, dictates a high plant bleed, and cuts production while increasing costs.
Partly in an effort to solve some of the foregoing problems, some SX processes have resorted to the use of coalescers in an attempt to perform an additional separation of the aqueous phase from the organic phase. While such coalescers are generally effective in removing additional amounts of entrained aqueous from the loaded organic, they are expensive and can be difficult to operate.
SUMMARY OF THE INVENTION
A method for separating a lighter liquid from a heavier liquid according to one embodiment of the present invention may comprise the following steps. First, the lighter liquid and the heavier liquid may be introduced into a settling tank and thereafter allowed to form a first upper liquid fraction and a first lower liquid fraction. The first upper liquid fraction may comprise the lighter liquid with residual amounts of the heavier liquid contained therein. The first upper liquid fraction is then decanted into a trough. The first upper liquid fraction decanted into the trough is then allowed to form a second upper liquid fraction and a second lower liquid fraction. The second lower liquid fraction may comprise the heavier liquid with residual amounts of the lighter liquid contained therein. The second lower liquid fraction is thereafter drained from the trough and allowed to form a third upper liquid fraction and a third lower liquid fraction.